The present invention relates to a process for producing an essential oil from a plant material. More particularly, the invention relates to a process for producing an essential oil, which is free of esters and consists essentially of terpene, in a short period of time and by a simple procedure involving extraction of an essential oil with water in a supercritical state or subcritical state.
Essential oils are volatile oils obtained from flowers, buds, leaves, branches, trunks, roots, etc. of various plants and having characteristic aromas. These oils are normally composed of several types of terpenes and aromatic compounds, and have osmophores such as alcohol, phenol and ester. Essential oils are utilized as raw materials for perfumes, and have been obtained by methods such as steam distillation, extraction, and expression.
Steam distillation is a method of distillation which, in the presence of steam, distills off liquids with high boiling points at considerably lower temperatures than the boiling points. Extraction is a method for dissolving certain components into a solvent, and separating and recovering the components. Expression combines squeezing with steam distillation or extraction with an organic solvent to obtain components in distilled form while squeezing the material.
In essential oils collected by these conventional methods, components containing esters are present. The esters are mainly acetic acid esters, which pose the problem of undergoing changes in properties owing to de-esterification which takes place during storage of the essential oils. There is also the drawback that the essential oils tend to undergo oxidative deterioration and acidic decomposition due to acetic acid per se which results from the de-esterification reaction. Furthermore, those conventional methods all give low yields, thus necessitating the use of multiple steps for treatment. Consequently, they are defective in that collection of essential oils by distillation cannot be completed in short periods of time. All of the conventional methods, moreover, possesses the shortcoming from an environmental viewpoint, that squeeze leavings of plant materials emerge as waste.
Various application studies are under way with regard to extraction, purification, synthesis and decomposition using supercritical fluids. For supercritical water, studies on its capacity to detoxify PCB and dioxin (Japanese Patent Public Disclosure (Kokai) No. 327678/97) are being carried out, and its degradation reaction of biomass is also being investigated. Japanese Patent Public Disclosure (Kokai) No. 31000/93 reports a method which selectively hydrolyzes or pyrolyzes natural or synthetic high molecular compounds with the use of supercritical water as a solvent to decompose the polymers into their constituent units or into approximately oligomeric combinations of the constituent units. Examples of this method include the formation of glucose from cellulose contained in large amounts in polymeric resources, such as paper, wood and straw, and conversion of lignin-derived specimens into low molecular compounds. Japanese Patent Public Disclosure (Kokai) No. 268166/97 describes a method for producing various amino acids by hydrolyzing proteins with water present in a supercritical state.
However, it has not been known that it is possible to obtain essential oils by treating plant materials with water present in a supercritical state.
It is an object of the present invention to provide a novel process for producing an essential oil from a plant material.
It is another object of the present invention to provide a process for producing an essential oil from a plant material, the essential oil being free of esters and consisting essentially of terpenes, and an essential oil produced by the process. According to the process of this invention, an essential oil having a composition unobtainable by conventional methods, such as steam distillation, can be provided.
It is a further object of the invention to provide a process for producing an essential oil, in which process an extraction procedure is completed in a very short time (within several minutes), as compared with conventional methods, such as steam distillation, generally used to obtain essential oils.
It is a still further object of the invention to provide a process for producing an essential oil, which process does not discharge waste generated as squeeze leavings as results from conventional methods such as steam distillation.
The present invention is a process for producing an essential oil in a short period of time and by a simple procedure, the process comprising treating a plant material with supercritical water or subcritical water to liberate essential oil components, which are contained in the plant material, as an ester-free essential oil; and separating and purifying the essential oil.
Examples of plants used to produce an essential oil in accordance with the present invention include, but are not restricted to, bamboo, Japanese cedar, hinoki, Quercus crispula, cherry tree, Japanese horse chestnut, pine tree, hiba arborvitae, Japanese chestnut tree, bamboo grass, oak, paulownia, Japanese apricot, peach, maple tree, zelkova tree, wisteria, fir, elm, ginkgo, camellia, willow, mulberry, magnolia, persimmon, apricot, Chinese quince, sweet brier, rose, loquat, Japanese quince, fragrant olive, camphor tree, Japanese yew, acacia, prickly shrub of Araliaceae, amyris, Boi de Rose, and loo. Depending on the plant selected, an essential oil having various scents is obtained. Two or more of these enumerated plants may be mixed and used in the invention.
Any parts of these plants can be used, such as trunk, bark, stalk, branch, root, leaf, flower, bud, and seed. Typically, a woody portion or a floral portion is used. For example, it is preferred to use wooded-type containers which were used for the production and/or storage of fermented products and foods and drinks, as plant materials, in order to effect utilization of waste materials.
A plant material from these plants may be treated, in any size, with supercritical water. Preferably, the plant material is chopped finely to a size of about 1 cm square, or if it is a floral portion, is cut thinly, for pretreatment, and then is subjected to supercritical water treatment. More preferably, the plant material is powdered, and then subjected to supercritical water treatment.
The process of the present invention is characterized by treating a plant material with supercritical water.
It is well known that substances can exist in three states:, as a solid, liquid or gas. If temperature and pressure are gradually increased, starting in a state in which a gas and a liquid mingle. When a certain pressure and a certain temperature (i.e., critical point) are exceeded, there exists a range in which the boundary surface between the gas and the liquid disappears, and the gas and liquid integrate as an inseparable entity, to form a fluid state. Such a fluid is called a supercritical fluid, which is a high-density fluid having properties intermediate between gas and liquid. That is, this fluid, like a liquid, dissolves various substances, and has high fluidity like a gas.
The critical point for water is a temperature of 374xc2x0 C. and a pressure of 221 atmospheres. Supercritical water refers to water in a state at a temperature and a pressure in specific ranges exceeding this critical point. Supercritical water continuously varies in the values of parameters, such as density, viscosity, dielectric constant, ion product, and diffusion coefficient, depending on temperature and pressure. Solubility, an important parameter for a reaction solvent, is known to increase as density increases. Another factor related to solubility is dielectric constant, which increases with increasing density, and decreases as temperature rises. At a sufficiently high temperature, a dielectric constant becomes so small that water is almost unable to shield the electrostatic force working among ions. Under these conditions, most of the dissolved ion species are present as ion pairs. Thus, supercritical water behaves as a nonpolar substance, rather than as a polar substance. Incidentally, the pH of water in a supercritical state is 4, producing a hydrogen ion concentration of {fraction (1/10,000)}, while the hydroxide ion concentration is also {fraction (1/10,000)}. Hence, it will be readily apparent that the properties of this water are entirely different from those of water as a liquid.
The present invention produces an essential oil by utilizing the foregoing features of supercritical water. The invention is characterized by the ability to produce an essential oil easily and-in a short time, in comparison with conventional technologies such as steam distillation. In light of this feature of the present invention, it can be easily predicted that treatment of a plant material with subcritical water next to supercritical water would similarly be able to obtain an essential oil. Hence, references, to be made hereinbelow, to supercritical water also include subcritical water, as will be clear from the context.
During supercritical water treatment, the plant material and water are mixed, for example, at a plant material-to-water ratio of 1:about 1 to 1,000, preferably, 1:about 5 to 200. The reactor may be any container suitable for supercritical water treatment, and may be selected, as desired, according to the scale of production. For example, a closed container (preferably one made of a metal such as SUS alloy) with a capacity of about 1 ml to 10 liters, preferably about 10 ml to 1 liter, is used. This container is charged with about 30 to 40% (V/V), preferably 32 to 35% (V/V), of water, and the plant material is added at the above-mentioned ratio. To produce an essential oil, treatment is preferably performed in an anaerobic state. For this purpose, it is advisable to deaerate the inside of the container, or fully purge the inside of the container and water with an inert gas such as nitrogen or argon, followed by closing the container. Treatment is performed under conditions under which water is in a supercritical state at a temperature of about 374xc2x0 C. (pressure at this time is about 221 atmospheres or more) to about 500xc2x0 C. (about 300 atmospheres or more), or under conditions under which water is in a subcritical state at a temperature exceeding about 300xc2x0 C. (exceeding about 150 to 200 atmospheres). The treatment time is within about 30 minutes, preferably within about 2 minutes.
The plant material treated with water in a supercritical state is cooled by a means such as rapid cooling of the reactor containing the material with iced water or the like. After making sure that the temperature has been sufficiently lowered, the reactor is opened. Normally, water soluble substances are recovered as an aqueous solution, while liposoluble substances adhere to the wall surface in a tarry form. Thus, the water surface is washed with water first, and then is sprinkled with a water-absorbing salt, such as anhydrous sodium sulfate or calcium chloride, for dehydration. Then, an essential oil is recovered with the use of a hexane-diethyl ether mixture (the mixing ratio is basically 1:1, but can be selected suitably depending on the plant material) as a solvent. Other examples of usable solvents are a petroleum ether-diethyl ether mixture, and a petroleum benzine-diethyl ether mixture. The recovered essential oil is purified, as required, with activated charcoal or an adsorbent carrier, and used according to the purpose of use. Purification methods rely on, but are not restricted to, various chromatographic techniques, use of various separation membranes, and use of various resins.
The thus obtained essential oil can be used, unchanged, as a perfume, or as a raw material for foods or cosmetics. Its application to pharmaceuticals can also be expected.
The tarry substance after extraction of the essential oil is likely to contain other useful components. For example, aromatic compounds, including phenylpropanoids, pyrogallol derivatives, and pyrocatechol derivatives, can be recovered by further extraction with organic solvents, such as alcohol, acetone and acetonitrile.
The aqueous solution recovered from inside the reactor may contain low molecular compounds such as glucose or lignin. These compounds may be isolated separately, if desired.